As a representative of the traditional building materials, concrete takes advantages of high compressive strength, high durability and low cost, widely used in industrial and civil buildings, bridges, road projects, underground projects, water conservancy and hydropower projects, nuclear power plants, ports and marine engineering etc. Currently, concrete has more than 100 years of history from it been invented, which penetrates to large-span structures, high-rise structures, mega-structure and the special structure.
The foreseeable future, during the country's modernization construction, concrete is still an indispensable building materials. Due to the use of long-term process and under the influence of the surrounding complex environment, in-service concrete structures is producing micro-cracking and local damage inevitably, which would reduce the life of the structures lightly, or would threaten structures safety. For raw materials, mixing ratio, additives, manufacturing processes, casting processes methods, and conservation area will be reviewed and improved, these methods didn't fundamentally change the performance of concrete weaknesses. Therefore, to repair the crack of the concrete in service timely and effectively has become a major concern of scientists and engineers. Due to earthquakes, wind loads, shock and other causes of damage, can visually detect and fix it manually, using traditional methods (program repair and post-restoration) on the crack repair. In the actual structure of concrete works, there are many small cracks, such as matrix micro-cracking etc, these micro-scale damages due to the limitations of detection technologies may be undetectable.
Therefore, it becomes very difficult to repair these undetectable cracks and damages, if not impossible. If the cracks or damages cannot be timely and effectively restoration, the structure will not only affect the normal use of the performance and shorten the life, but also macro-cracks may be triggered and led to structural brittle fracture, resulting in serious catastrophic accidents. There is an urgent need to adopt a certain technology or method, can take the initiative to automatically part of the crack and damage repairing, restore or even increase the strength of concrete materials in order to achieve the purpose of extending the service life of concrete structures. Existing technologies can not improve the solution of concrete micro-cracks self-diagnosing and self-repairing the problems. The self-repairing of the concrete is conducted by adding special components (such like shape memory alloy) to form intelligent self-repairing system that can be automatically triggered to fix the damage or crack of the concrete material.
Self-repairing concrete structures are currently concentrated in the hollow fiber restoration techniques, although in the laboratory technology, hollow fiber capsules was proved to be have self-repairing concrete function, but the construction process of concrete vibrator etc would disturb the arrangement of hollow fiber capsule design, and even lead to rupture of the glass wall material, the premature loss of repairing agent, would be unable to attain the purpose of repairing concrete and affect the feasibility of self-healing process of concrete and self-repairing capacity of the repeatability. During conservation and usage process, micro-cracks and cracks in concrete structures appeared in large numbers, randomly, self-repairing technical requirements for repair capsules evenly distributed in the concrete structure. Due to the brittle restrictions of hollow fiber material, hollow fiber capsules cannot use current technologies to ensure micro-capsule material evenly distributed in the concrete structure, so that, during the concrete structure micro-cracks self-healing process can only adopt special concrete materials and special process, such as self-compacting high performance concrete and non-chopped and crafts. These difficulties limit the hollow fiber capsules crack in the concrete structure of the effectively application of self-repairing works. Hollow fiber capsule's surface properties, wall materials strength, geometry parameters and content on the repair of concrete have significant impacts. Capsule fibrous wall material is smooth, which isn't easy to concrete form an effective phase interface, resulting in lower bond strength of concrete. Hollow fiber capsule has large size, diameter up to millimeters sometimes, which can be considered in the concrete structure, the introduction of fixed agent also inevitably introduces defects, reducing the concrete's own strength and self-healing efficiency. Hollow fiber capsule wall material has large glass strength, micro-cracks of concrete generated by stress, may be difficult to provide enough energy to make hollow fiber capsule rupture, thus, the use of the this technology may only fix large cracks, while micro-crack as the most critical factor for the concrete structure damage fracture repair may be limited. This method shows many problems to be solved in engineering applications, including the fibrous capsule durability, repairing timeliness, interface compatibility, reliability and engineering application of the feasibility of restoration and other issues. Early repair of micro-cracks for the durability of concrete structures is essential, so the use of hollow fiber micro-capsule technology does not apply to repair cracks, which has great limitations.